msm: kgsl: Correctly save the process mem entries in snapshot

All the mem entries were being written to a single location hence
the snapshot consisted of only the last mem entry of the process.
Fix this by writing each mem entry to consecutive location in the
snapshot.

Change-Id: I1971fc4b3adce3146768862a56db2b11c6ac44c4
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>